Cloning of Human insulin in a bacterial host

    Gene segments corresponding to the mature A & B chains of insulin are engineered into separate bacterial plasmids with an antibiotic resistance gene and a B-gal structural gene as markers.  The plasmids are separately transformed into E. coli.  Culture of the E. coli in the presence of antibiotics selects those cells that have been successfully transformed.  Induction of the B-gal gene expression (by addition of B-galactose sugar) also causes transcription of the insulin genes, which are then translated by the bacterial cells. The bacterial culture is done on an industrial scale to produce thousands of litres of cloned human insulin.

    Following chemical cleavage and purification away from the plasmid protein, the A & B chains spontaneously assemble to form biologically-active insulin. As this process in vitro is relatively inefficient, commercial human insulin is now made by cloning the proinsulin mRNA (without the signal peptide of pre-proinsulin) in a single host, and specific cleavage with the proteolytic enzymes.

Figure after © 2000 by Griffiths et al. ; All text material ©2011 by Steven M. Carr